In an evolution process of an Long Term Evolution (LTE) system, a project was set up in September, 2014, for researches on LTE Release 13 (Rel-13), where an important content is use of an unlicensed carrier by an LTE system for work. An unlicensed carrier, i.e., a license-exempt spectrum, refers to a spectrum or carrier which may be directly used without any license under the condition that a relevant regulation (radio control) of a government department (for example, the State Radio Regulatory Commission) is met. For example, a present 5 GHz frequency band belongs to an unlicensed carrier. Such a technology will enable an LTE system to use a present unlicensed carrier, thereby greatly improving a potential spectrum resource of the LTE system and enabling the LTE system to achieve lower spectrum cost. However, an LTE system may be confronted with many problems when using an unlicensed carrier. At first, in some countries and regions, there are corresponding control policies for use of unlicensed spectrums. For example, in Europe, if operating in an unlicensed carrier, an LTE system is required to support a Listen Before Talk (LBT) mechanism, and may occupy a channel only when a monitoring result is that the channel is idle.
For a present LTE protocol, there exist two types of CSI feedback: periodic CSI feedback and nonperiodic CSI feedback. For an unlicensed carrier, because of existence of an LBT mechanism, it is uncertain about whether a pilot configured for CSI measurement may be sent on the unlicensed carrier on a fixed subframe or not, and it is also uncertain about whether a Physical Uplink Shared Channel (PUSCH) or Physical Uplink Control Channel (PUCCH) containing a CSI feedback may be fed back on the unlicensed carrier or not. Therefore, a present periodic CSI feedback mechanism for a licensed carrier fails to be used any longer. Considering a characteristic of the LBT mechanism for the unlicensed carrier, a mechanism similar to nonperiodic CSI feedback is more suitable for the unlicensed carrier.
In a present protocol version LTE R10, an indication about nonperiodic CSI feedback is sent in a DCI format 0/DCI format 4, the DCI format 4 may provide a good support for multiple carriers and multiple uplink streams, and by indication of a carrier indicator and CSI request character therein, a terminal may learn about carriers on which nonperiodic CSI feedback is required to be performed and a carrier on which a PUSCH is to be sent.
High-layer Radio Resource Control (RRC) signaling may semi-statically notify a terminal of a candidate carrier set, the terminal may learn about a carrier set corresponding to nonperiodic CSI feedback according to indication of a CSI request character, and then the terminal may perform CSI measurement on these carriers and feed back CSI of these carriers in a preset subsequent subframe. From such a mechanism, it can be seen that there may exist such conditions on an unlicensed carrier that CSI fails to be measured, a PUSCH fails to be sent due to a failure in contention for a channel and the like.
For the technical problem that CSI of an unlicensed carrier fails to be measured in a related technology, there is yet no effective solution.